The present invention relates to apparatuses and methods for improving mobile communication. More particularly, the present invention relates to novel cellular private branch exchange apparatuses and methods that advantageously improve communication quality and network bandwidth, while simplifying implementation, maintenance, and upgrade.
Wired and wireless private branch exchanges (PBX's) are known in the art. FIG. 1 shows in a simplified diagram a wireless private branch exchange system (wPBX) of the prior art, including a wPBX 100. WPBX 100 is coupled to a line 102, which typically couples to a public network. WPBX 100 is further coupled to lines 104 and 106 as shown in FIG. 1. Line 104 is coupled to a base unit 108 while line 106 is coupled to another base unit, which is omitted from FIG. 1 for simplicity of illustration. Base unit 108 includes an antenna 110 to facilitate cordless communication with a plurality of cordless handsets 112 and 114. In the typical wireless wPBX system of the prior art, each base unit, such as base unit 108, typically controls two cordless handsets.
Although the wireless wPBX system of the prior art offers advantages associated with cordless handsets, there are several significant disadvantages. For example, a cordless handset in the prior art wireless PBX has no roaming capabilities. Roaming is not possible in the prior art wireless PBX, the cordless handsets do not have the capabilities to make the exchange between PBX's. This is partly because, in normal cordless applications, frequencies are not coordinated between wireless PBX systems.
To illustrate, consider the situation when cordless handset 112 travels outs of the range of base 108. When cordless handset 112 roams outside of the range of base 108, the data stream, whether it be voice or digital information, is cut off. This is because each cordless handset in the wireless wPBX of the prior art is associated with a particular base unit of a particular wPBX and cannot use the resources of any other base unit to make its calls. In wireless PBX systems, the telephone number is associated with a given frequency which is associated with a fixed port on the PBX. From the point of view of the PBX, therefore, the cordless handset is fixed to a PBX port just as in normal wired PBX's.
As mentioned earlier, cordless handsets of the prior art wireless PBX have no roaming capabilities. Further, there are also no roaming or hand-off capabilities in the wireless PBX units, e.g., wPBX 100, since prior art wireless PBX's do not possess the capabilities to coordinate with other PBX's to perform the roaming function. In other words, even when wPBX 100 is interconnected in a wPBX network, cordless handset 112 cannot be taken to another location controlled by another wPBX unit and make and receive calls and be associated with the same phone number without having to undergo administrative moves and changes, e.g. reprogramming the wPBX itself. Consequently, the range of each cordless handset is limited by the range of the base unit of the prior art wPBX with which it is specifically associated.
Another disadvantage of the prior art wireless wPBX systems of the prior art involves the use of low-power and proprietary transceivers, which significantly limit the range from which a cordless handset can be taken from its associated base.
Further, when calls are made among cordless handsets of the same wPBX, the call paths are typically switched, or cross-connected, at the wPBX level. In other words, the actual switching is centralized at the prior art wPBX even if cordless handsets of the same base unit desire to communicate among themselves, e.g., between cordless handsets 112 and 114. When calls are always switched at the highest level of the hierarchy, call paths to and from the cordless handsets are oftentimes unnecessarily back hauled all the way to the highest level, i.e., the wPBX, although it may be more efficient to cross connect closer to the cordless handsets, i.e. at a base unit at a lower level of the hierarchy. This is because wPBX unit 100 of the prior art lacks the intelligence necessary to delegate the switching function from wPBX unit 100 down to subsystems below it in the hierarchy, e.g., to base 108.
From the perspective of wPBX 100 or the public network to which link 102 is coupled, the fact that cordless handsets 112 and 114 communicate with base 108 in a cordless manner is irrelevant. Since there is no roaming and no hand-off capabilities between bases or wPBX's, the manner in which cordless handsets 112 and 114 are coupled to base unit 108 does not provide the user with any additional advantages besides the fact that cordless handsets 112 and 114 may be made cordless inside the range defined by the transceiver within base unit 108. Because of these limitations, the radius of operation of the prior art cordless handsets is typically limited to around 200 meters.
What is desired is an improved method and apparatus for providing mobility via standardized mobile handsets. To facilitate greater range, it is desirable that the improved method and apparatus employs cellular technology for the transmission of voice and data to and from the mobile handsets. To further increase range, the improved method and apparatus preferably permits its mobile handsets to roam among location areas in its domain. Furthermore, the improved method and apparatus preferably performs mobility management, call control, and radio resource management of its mobile handsets in a manner that is transparent to the public network to which it may be connected.
Furthermore, it is preferable that the improved method and apparatus avoids the unnecessary back hauling of data traffic to upper levels of the hierarchy merely for the purpose of accomplishing the cross connection. To improve the system bandwidth, it is preferable to cross connect call paths in an optimum manner at lower levels of the hierarchy. For ease of implementation, maintenance, and upgrade, it is desirable that the improved method and apparatus be implemented in a highly modular and scalable manner.